1. Field of the Invention
This invention relates to hydraulic underground mining systems. More particularly, this invention relates to hydraulic borehole underground mining accomplished by a high pressure liquid jet nozzle movable in vertical and circular directions to cause formation of a slurry, which is removed to the surface by means of a jet pumping apparatus.
2. Description of the Prior Art
Known methods for borehole mining of unconsolidated ores, such as phosphates or uranium, require predrilling a borehole into the ore formation and lining the borehole with a casing if the overburden is unconsolidated material. A mining tool inserted through the borehole serves to disintegrate the ore by jetting a mining fluid, usually water, into the ore formation. A slurry is thus formed which contains the mining fluid and ore in suspension and which is pumped upward through the mining tool to the ground surface. Prior art methods include jet pumps located in the lower portion of the borehole to receive a supply of high pressure fluid from the surface and also include force pumps located at the lower portion of the borehole with the force pumps receiving either hydraulic or electrical power from the surface.
Hydraulic borehole mining systems have not been widely used due to a number of problems which arise in their implementation. If a mechanical force pump is located in the lower portion of the borehole, the construction and operation of the mining tool is greatly complicated. Mechanical force pumps are prone to break down, requiring frequent servicing, which, if the pump is located in the lower portion of the borehole, requires removal, repair and reinsertion of the mining head with consequent expense and loss of time. If jet pumps are used to lift the slurry from the mining area, large quantities of high pressure water are required for the powering of the pump, resulting in a dilute slurry which is expensive to separate into its component parts. Bore hole mining systems currently in use require removal of the mining tool to position the cutting jet in a vertical direction. U.S. Pat. No. 3,797,590, reissued as U.S. Pat. No. Re. 29,021, illustrates a bore hole mining system which allows partial movement of the cutting jet in a circular path; but the cutting jet is not rotatable for more than a portion of an arc; and the mining tool must be lifted to move the cutting jet in the vertical direction. Easy mobility of the cutting jet is of great economic benefit in the mining of minerals such as uranium where the ore is found in isolated lensatic deposits. Current bore hole mining systems also do not provide means for monitoring the condition of the bore hole or indicating the degree of completion of mining of an isolated formation. The lack of complete monitoring apparatus complicates the control of the operation of the borehole mining system, increasing labor costs and time required to mine the formation. Borehole mining systems currently in use are limited to mining of unconsolidated formations such as phosphate ores. The above-mentioned problems have prevented the wide-scale adoption of borehole mining system in other than the specialized cases noted above.